In late January I am travelling to Iceland for 4 days and the Netherlands, possibly other countries in the region until I return home (looking to be 2nd Thursday in March).

The other countries are in the EU but I'm expecting to spend a longer time in the Netherlands than any other single country. I was hoping to get a local Dutch SIM for Netherlands & maybe Vodafone UK or T-Mobile UK or whoever have the best European roaming bundle for non-NL/non-UK use. I looked on Vodafone & KPN's site and while there doesn't appear to be any sort of weekly or monthly data bundles in their English section, I have noticed Vodafone BloX on that site in their prepaid section. Is Vodafone BloX the best deal for someone who normally uses around 300 to 1000 MB/month? I'm willing to get more than one Dutch SIM if for instance voice is much cheaper on another SIM. I regularly walk around with more than one phone anyway.

Any experienced users here regularly in these parts?

Within the Netherlands, I'm hoping to be travelling around various cities, particularly Amsterdam, The Hague, Rotterdam, Utrecht, & Zeeland (mentioning in case coverage is widely different from place to place). The phone I'll be using for local data (Motorola Flipout MB511 from Orange UK) has 3G 900/2100 MHz & quadband 2G. Another phone (Sony Ericsson Z750a, debranded to Z750i) I have which I want to do only local GSM voice on has 850/1900/2100 MHz 3G & quadband 2G.

I hope to stay in touch with people back home in the US using VoIP over either mobile or WiFi data. I have both a Google Voice & Skype account that has an unlimited US/Canada subscription + number. Should the Skype work fine from abroad? On either WiFi or mobile? If so, about how much bandwidth would a typical voice call be using per minute?

I haven't done much research on Dutch providers but one quite interesting offer is T-Mobile's "prepaid Internationaal" tariff, which gives you unlimited internet access for  2.50 day (limited to 384 KBit/s down- and 64 KBit/s upstream, tethering allowed) and decent domestic and international calling rates. According to their tariff calculator calls to the UK cost  0.12/min to fixed lines and  0.39/min to mobiles. However since they accredit the double amount for each recharge (you get  20 of credit for a  10 recharge) calling rates to the UK are virtually  0.06/min to landlines and  0.195/min to mobiles.
I have two spare of these T-Mobile Internationaal SIMs, one with  0.06 and the other with  21.58 remaining credit, which I would sell you for the amount of the remaining credit +  2.80 insured shipping with tracking + PayPal fees, since I won't visit the Netherlands soon.
Btw the Dutch run UMTS only at 2100MHz and GSM at 900/1800 MHz - so no need for multiband devices there.